One method is to get on the gun, have the plumb line and have a buddy move the scope as you are on the gun, meaning shouldered and held as if you would shoot it. Remember and this is a rabbit hole, the gun under recoil will find the weak spot, if you are muscling the gun onto the target it will under recoil want to return to the natural point of aim if it's not there at the start. Know how to adjust the NPA and obtain bone support and make it repeatable.

Not to debate any scope mounting method. Mechanically leveled, depending on the shooter they will get on the gun and say "my scope is crooked" It's because it's going into the shoulder differently, hence the adjustable butt plates.

Again, many methods and styles.